Glacial Lake Outburst Flood Modelling of the Tikip Lake, Sikkim Himalaya, India

Glaciers in the Himalaya are experiencing a high rate of melting due to ongoing climate change. The melting waters of the glaciers accumulate in depressions, forming high-volume glacial lakes. Natural causes, such as ice avalanches and the collapse of a moraine dam in the lake, are widely considered major triggering factors for Glacial Lake Outburst Floods (GLOFs). In this study, Tikip Lake, one of the high-risk glacial lakes located in the Gyalshing district of Sikkim, was selected to model the GLOF process chain for the worst-case scenario using Rapid Mass Movement Simulation (RAMMS) Avalanche and Hydrologic Engineering Center's River Analysis System (HEC-RAS) (version 6.6) dam break models. The HEC-RAS dam break model yielded peak discharges of 6072 m 3 /s and 4050 m 3 /s for the overtopping and piping modes of moraine dam failure, respectively. Overall, the total inundation areas are 4.03 and 3.82 km 2 for overtopping and piping modes, respectively. Furthermore, an analysis of discharges and flood extents for overtopping and piping modes suggests that the Tashiding dam, Tashiding hydroelectric plant (HEP), 17 buildings, and 5 bridges, a road length of 220m, as well as 18000 m 2 of farmland, have a very high damage potential under both scenarios. The shear stress of the flow under both the dam failure modes is also very high, which could erode the valley laterally and the bedrock of the valley floor. As a consequence, this may generate hyper-concentrated flow that could have the potential to cause severe damage to Rangeet Dam-III. The findings of this study can be utilized for planning structural and non-structural measures to minimize the potential damage to infrastructures located in the downstream areas of the lake. • Tikip Lake has been increasing rapidly since 1990 due to a sharp temperature rise. • The steep eastern tributary of the Kokthang Glacier is highly prone to an ice avalanche. • Overtopping and piping failure modes of the moraine dam may yield peak discharges of 6072 m 3 /s and 4050 m 3 /s, respectively, under the worst-case scenario. • Tashiding Dam, Tashiding HEP, 17 buildings, 5 bridges, a 220-meter road, and 1.8 hectares of farmland are at a very high risk of damage.